This application is based on patent application No. 2000-050253 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a semiconductor wafer manufacturing method capable of removing a deteriorated layer formed on the surface or in the interior of a semiconductor wafer such as silicon wafer.
2. Description of the Related Arts
Generally, in this type of a semiconductor wafer manufacturing method, as shown in FIG. 12, there are adopted a slicing process 100, a planarizing process 101, and an etching process 102.
More specifically, first in the slicing process 100, an ingot of a single silicon crystal is cut in a disc shape using a cutting tool such as an edged tool or a wire saw to afford a semiconductor wafer. In this process, concaves and convexes conforming to the edge shape of the cutting tool used are formed on the wafer surface and a deteriorated layer is formed to a depth of about 25 to 50 xcexcm from the wafer surface. For leveling the wafer surface there is performed the planarizing process 101.
The planarizing process 101 is for removing the concaves and convexes which have been formed on the wafer surface in the slicing process 100 and thereby leveling the wafer surface. In the planarizing process, the wafer surface is subjected to lapping or polishing with use of a double-side polishing machine of a mechanical structure. In this planarizing process it is possible to attain the planarization of the wafer surface, but the removal of a deteriorated layer cannot be done to a satisfactory extent and there remains a deteriorated layer of a depth of about 10 to 15 xcexcm from the wafer surface.
The etching process 102 is conducted for the purpose of removing the remaining deteriorated layer.
Heretofore, in this type of etching process 102 there has been adopted a wet etching process such as acid etching or alkali etching.
In the acid etching process, a wafer is dipped in a mixed solution of nitric acid (HNO3) and hydrogen fluoride (HF), allowing silicon (Si) of the wafer to be oxidized with nitric acid to afford silicon oxide (SiO2), which is then dissolved off with hydrogen fluoride. In this process, an etching reaction is carried out at diffusion-determined speed. Therefore, for keeping the etching speed for the wafer surface as uniform as possible, the wafer is rotated in the solution or bubbling of the solution is performed.
On the other hand, in the alkali etching process, the wafer surface is etched using an alkali solution such as KOH or NaOH to remove the deteriorated layer.
For upgrading the wafer to a further extent there sometimes is adopted a polishing process 103, as shown in FIG. 12.
The polishing process 103 is for mirror-polishing the wafer surface. In this process, mirror-like polishing is performed in plural stages, including first, second and finishing stages, to improve the flatness of the wafer surface and enhance the removing efficiency for ripple, haze and roughness component called microroughness.
In the above conventional semiconductor wafer manufacturing method, however, since there is adopted a wet etching process, there is the problem that the wafer flatness is impeded, although the deteriorated layer can be removed.
More particularly, in the acid etching process, as noted above, since the etching reaction is carried out at diffusion-determined speed, the wafer is rotated in the etching solution or bubbling of the solution is performed to keep the etching speed for the wafer surface as uniform as possible. But even by such means it is still impossible to keep the etching speed uniform to a satisfactory extent. For ensuring uniform etching it is necessary to precisely control the concentration and flow velocity of the acid etching solution used. However, it is actually difficult to make the concentration and flow velocity of the solution at the central and nearly portions of the wafer equal substantially completely to the concentration and flow velocity of the solution at the outer peripheral and nearby portions of the wafer. Consequently, the etching speed differs to an unignorable extent between the central portion and the outer peripheral portion of the wafer, thus impeding the flatness of the wafer surface.
That the dilution effect of the solution based on the formation of a reaction product in acid etching differs at various positions of the wafer also impedes the attainment of uniform etching. This tendency becomes more and more conspicuous as the wafer diameter increases. This point is a great negative factor in improving the flatness of a wafer 300 mm in diameter.
Further, the mixed solution of nitric acid and hydrogen fluoride is very unstable chemically and the storage thereof is very difficult.
In the alkali etching process, unlike the acid etching process, such a non-uniform etching caused by a bias in both solution concentration and flow velocity as in the acid etching does not occur, but there is the problem that so-called etch pits are formed on the wafer surface.
More particularly, when such a caustic alkali as KOH or NaOH etches the wafer surface in the wafer thickness direction, the etching speed differs, depending on the crystal orientation of silicon, that is, the caustic alkali exhibits anisotropy in a certain crystal orientation, with the result that etch pits are formed on the wafer surface after etching.
Besides, the tendency toward a larger wafer diameter is giving rise to a correspondingly increased consumption of both acid and alkali solutions, thus inevitably requiring an increase of equipment for treating the resulting waste fluids.
Further, with the recent demand for upgrading the wafer, restrictions against impurities, e.g., metal contamination, are also becoming more and more strict, and additional costs are now required for improving the purity of the etching solution to be used and for the maintenance and storage thereof.
The present invention has been accomplished for solving the above-mentioned problems and it is an object of the invention to provide a method for manufacturing a semiconductor wafer of high quality which method adopts a novel dry etching process and thereby can remove a deteriorated layer, ensure flatness and prevent the occurrence of etch pits.
The semiconductor wafer manufacturing method of the present invention comprises a slicing process for slicing an ingot of a single silicon crystal to afford a wafer for semiconductors, a planarizing process for lapping or polishing a surface of the wafer obtained in the slicing process to flatten the wafer surface, and a dry etching process for removing a deteriorated layer from the wafer by spraying a neutral active species locally to the surface of the wafer obtained in the planarizing process. The dry etching process comprises a plasma generating step by allowing a halogen-containing compound gas contained in a discharge tube to be discharged to generate plasma containing a neutral active species, an active species conveying step for separating the neutral active species from the plasma by conveying the plasma gas to an orifice side of a nozzle portion of the discharge tube, and spraying the neutral active species locally to the wafer surface opposed to the nozzle orifice, and a deteriorated layer removing step for moving the nozzle portion of the discharge tube relatively along the wafer surface to etch off the deteriorated layer of the wafer.
According to this construction, in the slicing process, an ingot of a single silicon crystal is sliced in the shape of a semiconductor wafer, then in the planarizing process the wafer surface is subjected to lapping or polishing and is leveled thereby.
Lastly, in the dry etching process, the deteriorated layer of the wafer is removed. To be more specific, in the dry etching process, the plasma generating step is carried out, whereby a gas of a halogen-containing compound present within a discharge tube is discharged and plasma which contains a neutral active species is generated within the discharge tube. Then, the active species conveying step is carried out, whereby the neutral active species is separated from the plasma while conveyed to the nozzle orifice side of the discharge tube and is sprayed locally to the wafer surface opposed to the nozzle orifice. Subsequently, the deteriorated-layer removing step is carried out, whereby the nozzle portion is moved relatively along the wafer surface and the deteriorated layer of the wafer is etched off.
As the gas added in the plasma generating step in the dry etching process there is used at least one of oxygen gas, hydrogen gas, and ammonia gas.
Further, between the planarizing process and the dry etching process is provided a heating process of heating the wafer having gone through the planarizing process to a temperature of above 60xc2x0 C. and below 350xc2x0 C.
Further, the dry etching process includes a temperature controlling step of making control so as to heat one side of the wafer to which the neutral active species is sprayed to a temperature of above 60xc2x0 C. and to cool another side to a temperature not exceeding 350xc2x0 C.
Further, in these semiconductor wafer manufacturing methods there is provided a polishing process for mirror-polishing the wafer surface which has been treated in the dry etching process.
According to the semiconductor wafer manufacturing method of the present invention, the neutral active species generated in the plasma generating step of the dry etching process is sprayed locally to the wafer surface from the nozzle orifice of the discharge tube in the active species conveying step, then in the deteriorated layer removing step, the nozzle portion is moved relatively along the wafer surface to etch off the deteriorated layer of the wafer, and thus the deteriorated layer can be removed while etching the wafer surface flatways. Besides, unlike the conventional acid etching technique, there does not occur the phenomenon that the dilution effect of solution caused by the creation of a reduction product differs at various positions of the wafer. Consequently, even such a large size of wafer as 300 mm in diameter can be dry-etched while retaining its flatness.
Moreover, since there is adopted the active species conveying step of conveying the neutral active species to the orifice side of the nozzle portion and spraying it locally to the wafer surface opposed to the orifice, the etching speed of the neutral active species for the wafer exhibits isotropy and is thus not influenced by the crystal orientation of the wafer. As a result, it is possible to prevent the occurrence of etch pits which has been a problem in the conventional alkali etching technique.
Further, since the gases used in the dry etching process are a halogen-containing compound gas and an additive gas such as oxygen gas, hydrogen gas, or ammonia gas, the gases can be stored safely and easily by charging them respectively into gas cylinders. Also, since the product produced in the process is gaseous, a disposal equipment of a small size and a simple structure will do. Additionally, since there is no fear of metal contamination of the wafer, it is possible to omit the management cost for the prevention of metal contamination and thus the total maintenance and management cost can be so much reduced.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.